Radio wave receiver

ABSTRACT

Disclosed is a radio wave receiver including an antenna to receive a radio wave, a tuning unit to switch a frequency characteristic of the antenna in a stepwise fashion, an oscillation unit to oscillate the antenna and a circuit section of the tuning unit, a receiving process unit to carry out a signal process by extracting a signal of a desired wave among received signals which are received from the antenna, a search control unit in which the oscillation unit is made to generate an oscillation signal at the circuit section and in which the oscillation signal searches a setting condition of the tuning unit which is extracted in the receiving process unit by switching a setting of the tuning unit and a search range deciding unit to selectively decide an adjustable range in which the switching of the setting of the tuning unit is carried out by the search control unit so as to be a specific adjustable range which is a portion of an entire adjustable range of the tuning unit corresponding to a frequency of the desired wave.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radio wave receiver comprising anantenna and a tuning unit.

2. Description of Related Art

Conventionally, there is suggested a communication apparatus which makesthe resonance frequency of an antenna tune to the frequency of a desiredwave by changing frequency characteristic of a tuning circuit connectedto the antenna (for example, Japanese Patent Application Laid-OpenPublication No. 11-312958 and Japanese Patent Application Laid-OpenPublication No. 2000-231609). Further, Japanese Patent ApplicationLaid-Open Publication No. 11-312958 discloses a technique in which thesize of tuning capacitance can be switched continuously and finely bycarrying out weighting to the capacitance values of a plurality ofresonance condensers which can be connected and can be cut-off in anantenna circuit to arbitrarily switch the resonance condensers.

When the adjustment of tuning capacitance can be finely set, a long timeis required to search for the optimum setting condition by carrying outswitching of the tuning capacitance one step at a time for the entireadjustable range because the number of steps to switch the settingincreases.

An object of the present invention is to provide a radio wave receiverwhich can shorten the process time by effectively carrying out theswitching of the setting of the tuning circuit when searching for theoptimum setting condition of the tuning circuit.

SUMMARY OF THE INVENTION

One of preferable embodiments of the present invention is a radio wavereceiver comprising an antenna to receive a radio wave, a tuning unit toswitch a frequency characteristic of the antenna in a stepwise fashion,an oscillation unit to oscillate the antenna and a circuit section ofthe tuning unit, a receiving process unit to carry out a signal processby extracting a signal of a desired wave among received signals whichare received from the antenna, a search control unit in which theoscillation unit is made to generate an oscillation signal at thecircuit section and in which the oscillation signal searches a settingcondition of the tuning unit which is extracted in the receiving processunit by switching a setting of the tuning unit and a search rangedeciding unit to selectively decide an adjustable range in which theswitching of the setting of the tuning unit is carried out by the searchcontrol unit so as to be a specific adjustable range which is a portionof an entire adjustable range of the tuning unit corresponding to afrequency of the desired wave.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an entire radio wave receiver of anembodiment of the present invention.

FIG. 2 is a table showing an example of capacitance values of aplurality of capacitative elements which are provided in a tuningcircuit.

FIG. 3 is a graph showing relation between counter values which decideswitching condition of the tuning circuit and resonance frequency of theantenna.

FIG. 4 is a graph conceptually expressing an example of search ranges inthe antenna adjustment process corresponding to each of the receivingchannels.

FIG. 5 is a flowchart showing a controlling procedure of the antennaadjustment process which is executed by a CPU of a control circuit.

FIG. 6 is a table showing an example of search ranges corresponding toeach of the receiving channels.

FIG. 7 is a table which explains difference between a case whereconnection of the minimum capacitative element C0 is switched and a casewhere connection of the minimum capacitative element C0 is not switchedin the antenna adjustment process.

FIG. 8 is a diagram showing an example of data stored in a ROM in aradio wave receiver of other embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be describedbased on the drawings.

FIG. 1 is a block diagram showing an entire radio wave receiver of theembodiment of the present invention.

The radio wave receiver 1 of this embodiment is a device to receive aradio wave and to carry out a demodulation process of an informationsignal included in a signal of a desired wave. In particular, the radiowave receiver 1 is a device to receive a standard radio wave in whichtime code is included, which is installed in an electronic watch. Theradio wave receiver 1 comprises an antenna 10 to receive a radio wave, atuning circuit (tuning unit) 11 to adjust frequency characteristic ofthe antenna 10, a RF circuit 12 to carry out amplification and noiseremoval of the RF signal received by the antenna 10, a filter 13 toextract the frequency signal of the desired wave from the receivedsignal, an amplifier 14 to amplify the extracted frequency signal of thedesired wave, a detector circuit 15 to detect an output of the amplifier14 and regenerate the information signal, a feedback circuit 16 as anoscillation unit which can cause a loop oscillation at the antenna 10and at the circuit section of the tuning circuit 11 by feeding back theRF signal, a control circuit (search control unit) 20 to execute anadjustment process and the like of the antenna 10 and the like.

Among the above structures, a receiving process unit to extract thesignal of the desired wave to carry out a signal processing isstructured by the filter 13, the amplifier 14 and the detector circuit15.

The antenna 10 is a bar antenna which is formed by a coil being wrappedaround a core, for example, and alternatively, a monopole antenna, adipole antenna or the like can be applied according to the frequency tobe received. The band characteristic of signals which can be received bythe antenna 10 has a characteristic where the receiving level reachesthe peak with the resonance frequency of the coupled circuit which isformed by the inductance component of the antenna 10 and the capacitancecomponent of the tuning circuit 11 joining with each other and thereceiving level decreases as the frequency deviates from the resonancefrequency.

The tuning circuit 11 comprises a capacitative element C9 which isfixedly connected between both of the terminals of the antenna 10, aplurality of capacitative elements C0 to C8 which can be connected inparallel between both of the terminals of the antenna 10 and which cancut-off the connection and a plurality of switches S0 to S8 to switchconnect/cut-off of the capacitative elements C0 to C8, for example. Bycontrolling ON and OFF by arbitrarily combining the switches S0 to S8,the capacitance value of the tuning circuit 11 changes and the resonancefrequency of the resonance circuit which is joined with the inductancecomponent of the antenna 10 can be adjusted.

The RF circuit 12 is a circuit which includes a RF amplifier whichamplifies the received signal which is received via the antenna 10, afilter for noise removal and the like.

The filter 13 allows a signal of the frequency of the desired wave amongthe signals received via the antenna 10 pass through and makes thesignals of other frequency attenuate. The filter 13 is structured by abandpass filter, a lowpass filter or the like being connected in cascadeconnection. The passing band of the filter 13 is structured with a verynarrow band width, for example, about 10 Hz, centering the frequency ofthe desired wave. The filter 13 is structured so as to be able to switchthe center frequency of the pass band between the frequencies of aplurality of receiving channels (for example, 40 kHz, 60 kHz, 77.5 kHz)based on the channel switching signal of the control circuit 20.

The feedback circuit 16 has an amplifier built-in, for example, andcauses oscillating movement at the feedback loop by amplifying theoutput of the RF circuit 12 by the amplifier and by feeding theamplified output of the RF circuit 12 back to the signal line of thetuning circuit 11. The feedback circuit 16 is connected to the signalline via the coupling condenser about a size which does not influencethe frequency characteristic of the antenna 10 and the tuning circuit11, and the oscillation frequency of the feedback loop is about the sameas the resonance frequency of the antenna 10 (the resonance frequency ofthe resonance circuit in which the antenna 10 and the tuning circuit 11are joined). Further, the feedback circuit 16 can be switched betweenoperation state and non-operation state by turning on and turning offthe supply of power voltage by a switch, for example.

Here, the structure of the feedback circuit 16 can be modifiedvariously. For example, regarding where the signal is to be fed back viathe feedback circuit 16, it can be structured so that the signal is tobe fed back to the signal line wrapped around the antenna 10, forexample, as an alternative to the signal line of the tuning circuit 11.Further, the output of the RF circuit 12 may be differential signals andthe differential signals may be respectively fed back to each of a pairof signal lines of the antenna 10 or the tuning circuit 11. Furthermore,an auxiliary winding which is electromagnetically coupled with the coilof the antenna 10 may be provided and the signal may be fed back to theauxiliary winding, or an antenna for radiation may be provided and thesignal may be fed back to the antenna 10 as a radio wave. Moreover, itis possible to feedback the output of the RF circuit 12 directly to thesignal line of the antenna 10 or the tuning circuit 11 via the signalline for feedback without amplifying the signal at the feedback circuit16. In such case, by providing a switch element serially with the signalline for feedback and by turning this switch element on and off, it ispossible to control ON/OFF of the feedback operation.

The control circuit 20 has an AD converter, a CPU (Computer PeripheralUnit), a ROM (Read Only Memory) in which control data and controlprogram are stored, a RAM (Random Access Memory) which provides the CPUwith a memory space for working, a 9-bit counter to decide conditions ofthe switches S0 to S8 of the tuning circuit 11, an I/O circuit to outputa control signal outside and the like built-in. The AD converter carriesout AD conversion to the signal which is inputted to the input terminalADC and outputs the digital value thereof so as to be readable by theCPU. The I/O circuit outputs switching control signal of the switches S0to S8 according to the counter value of the 9-bit counter, outputs theON/OFF control signal to the feedback circuit 16 and outputs the channelswitching signal to the filter 13 by a command of the CPU.

In the ROM of the control circuit 20, a processing program of a radiowave receiving process to receive the standard radio wave and todecipher the time code, a processing program of an automatic adjustmentprocess of antenna to store the optimum setting condition of the tuningcircuit 11 by carrying out a setting adjustment of the tuning circuit 11for each of the receiving channels and the like are stored.

In FIG. 2, a table showing an example of capacitance value of each ofthe capacitative elements which are provided in the tuning circuit 11 isshown.

Regarding each of the capacitative elements C0 to C9 of the tuningcircuit 11, nine capacitative elements C0 to C8 which can be switchedbetween connect and cut-off, excluding the capacitative element C9 whichis fixedly connected, are designed so as to be increased approximatelyby power-of-two in order from the small capacitance value. For example,capacitance values shown in the table of FIG. 2 are set. Further, nineswitches S0 to S8 for respectively switching connection of thecapacitative elements C0 to C8 are made to correspond so as to beswitched according to each of the bit values of the 9-bit counterprovided in the control circuit 20. Each of the bits of the counter ismade to correspond respectively to the values from the small capacitancevalue to the large capacitance value in order of high order bit to lowerorder bit.

By the capacitance value of each of the capacitative elements C0 to C8as described above and by the structure of the 9-bit counter whichdecides the connection condition of the capacitative elements, the totalcapacitance value of the tuning circuit 11 which is coupled with theantenna 10 can be switched approximately in proportion to the countervalue of the counter. For example, when it is structures so that thecapacitance values of the capacitative elements C0 to C8 are increasedprecisely by power-of-two, the total capacitance value of the tuningcircuit 11 which is coupled with the antenna 10 can be switched almostconsecutively by an interval of minimum switching steps (for example,0.85 pF) from the minimum capacitance value (for example, 50 pF) whenall of the capacitative elements C0 to C8 are cut-off to the maximumcapacitance value (for example, 484 pF) when all of the capacitativeelements of C0 to C8 are connected.

In FIG. 3, a graph which expresses relation between counter value thatdecides switching condition of the tuning circuit 11 and resonancefrequency of the antenna is shown. In FIG. 3, the plot line which is theblack horizontal line is the characteristic line when the capacitativeelements C0 to C9 have ideal capacitance values, the square plot line isthe characteristic line when the capacitance values of the capacitativeelements C0 to C9 have an error of +20% and the triangle plot line isthe characteristic line when the capacitance values of the capacitativeelements C0 to C9 have an error of −20%. Further, the vertical axis ofthe graph of FIG. 3 indicates frequency (Hz) and the horizontal axisindicates counter value (decimal notation) which decides the switchingcondition of the switches S0 to S8. Here, in the embodiment, the signalvalue of the switch C0 which corresponds to the minimum capacitativeelement C0 is a value of first decimal point in binary notation, and the8-bit signal value of the switches S8 to S1 is expressed in decimalnotation as a value before decimal point.

As shown in FIG. 3, by the above described structure of the tuningcircuit 11, the resonance frequency of the antenna 10 is to changegently according to the counter value which decides the switchingcondition of the switches S0 to S8.

A constant (for example, about ±10%) product tolerance occurs in thecapacitance values of the capacitative elements C0 to C9 and theinductance value of the antenna 10. However, when the plurality ofcapacitance elements C0 to C8 are formed on 1-chip semiconductor, errorof each of the capacitative elements C0 to C8 will occur at a similarrate. Therefore, as shown in the square plot line and the triangle plotline of FIG. 3, the characteristic line of the resonance frequency ofthe antenna 10 changes its value so as to swing up and down as a wholewith respect to the standard characteristic line according to the errorof the capacitative elements C0 to C8. However, the characteristic ofchanging gently according to the counter value which decides theswitching conditions of the switches S0 to S8 does not change.

Thus, as shown in FIG. 3, by arbitrarily selecting the capacitance valueof each of the capacitative elements C0 to C9 of the tuning circuit 11according to the inductance value of the antenna 10, the resonancefrequency of the antenna 10 can be adjusted so as to suite each of thereceived frequencies of the plurality of channels (for example, 40 kHz,60 kHz, 77.5 kHz) by arbitrarily carrying out switching betweenconnect/cut-off of the capacitative elements C0 to C8 even when erroroccurs in the inductance value and the capacitance values.

Further, the resonance frequency of the antenna 10 is proportionate tothe reciprocal of square root of the capacitance value. Therefore, asshown in FIG. 3, when the total capacitance value which is to beswitched to the connected condition in the tuning circuit 11 changes ata constant step, the amount of change in step of the resonance frequencyof the antenna 10 is not constant and will be different according to thefrequency band. For example, in a range of high frequency, the amount ofchange in step of the frequency is large with respect to change in thecapacitance value at a constant step. In contrary, in a range of lowfrequency, the amount of change in step of the frequency is small withrespect to the change in the capacitance value at a constant step.

[Antenna Adjustment Process]

First, an outline of the antenna adjustment process will be described.The antenna adjustment process is a process to search the settingcondition of the tuning circuit 11 which tunes the resonance frequencyof the antenna 10 to the frequency of the desired wave.

In the antenna adjustment process, the feedback circuit 16 is constantlyin operation state during the process. When the feedback circuit 16 isin operation state, an oscillation loop is formed in a signal path ofthe RF circuit 12, the feedback circuit 16 and the tuning circuit 11 andan oscillation signal is generated at this section. In the oscillationloop, the circuit constant which becomes dominant to decide theoscillation frequency is the inductance of the antenna 10 and thecapacitance component of the tuning circuit 11. Therefore, the frequencyof the oscillation signal will be approximately same as the resonancefrequency of the coupled circuit of the antenna 10 and the tuningcircuit 11.

Further, in the antenna adjustment process, the CPU switches theswitches S0 to S8 of the tuning circuit 11 to switch the totalcapacitance value which is to be switched to the connected state in thetuning circuit 11 within a predetermined adjustable range while theoscillation signal is being generated. By this switching, the resonancefrequency of the antenna 10 and the frequency of the oscillation signalare also changed. Further, every time the frequency of the oscillationsignal is switched, AD conversion is carried out to the output level ofthe detector circuit 15 and the output level is detected. The operationwhere the setting of the tuning circuit 11 is switched while monitoringthe detector output level is called the search process.

Here, when the resonance frequency of the antenna 10 is deviated fromthe frequency of the desired wave by the switching of the setting of thetuning circuit 11, the oscillation signal having a frequencyapproximately equal to the resonance frequency is greatly attenuated bythe filter 13. Therefore, the level of detector output becomes small. Onthe other hand, when the resonance frequency of the antenna 10approximately overlaps the frequency of the desired wave by theswitching of the setting of the tuning circuit 11, the oscillationsignal having a frequency approximately equal to the resonance frequencypasses through the filter 13 and the level of detector output increases.

Thus, by the above search process, the CPU can obtain the settingcondition of the tuning circuit 11 in which the level of detector outputis at peak as the optimum setting condition to tune the resonancefrequency of the antenna 10 to the frequency of the desired wave.Further, by carrying out the above search process to each of theplurality of receiving channels, the optimum setting condition of thetuning circuit which corresponds to each of the receiving channels canbe obtained.

Moreover, in the antenna adjustment process of the embodiment, theadjustable range in which the setting of the tuning circuit 11 is to beswitched in the search process is to be narrowed down to a specificadjustable range (called search range) which is set to a portion withinthe entire adjustable range by making the adjustable range correspond tothe frequency of the desired wave of the receiving channel.

In FIG. 4, a graph expressing an example of the search range of theantenna adjustment process which corresponds to each of the receivingchannels is shown. In this graph, each pattern of detector output of aplurality of the receiving channels are conceptually shown, and thenumerical values shown by the graph lines and the change patters are notthe actual values and patterns.

As shown in FIG. 3, the tuning circuit 11 is structured to have a broadadjustable range so that the resonance frequency of the antenna 10 canbe tuned to all of the frequencies of a plurality of receiving channels.Therefore, when merely tuning the resonance frequency of the antennal 10to the frequency of a receiving channel (for example, 77.5 kHz), thereis no need to switch the setting within the entire adjustable range, andas shown in FIG. 4, the optimum setting condition of the tuning circuit11 corresponding to the receiving channel can be obtained even when thesearch range is narrowed down to a range around the adjusting pointcorresponding to the receiving channel. Therefore, in the antennaadjustment process of the embodiment, search process within an unneededadjustable range is omitted to shorten the process time by narrowingdown the search range so as to be corresponded to the receiving channel.Particular examples of each search range respectively corresponding toeach receiving channel will be described later.

Moreover, in the antenna adjustment process of the embodiment, when thesearch range is within a range where the resonance frequency of theantenna 10 becomes high, the capacitance value of the tuning circuit 11is to be switched by minimum switching steps by using all of thecapacitative elements C0 to C8 in which connection can be switched asthe first group of tuning condensers. On the other hand, when the searchrange is within a range where the resonance frequency of the antenna 10becomes low, the capacitance value of the tuning circuit 11 is to beswitched by the minimum switching steps taking two steps at a time byusing the capacitative elements C1 to C8, omitting the minimumcapacitative element C0, as the second group of tuning condensers.

As shown in FIG. 3, in the structure of the tuning circuit 11 and theantenna 10 of the embodiment, the amount of change in the resonancefrequency of the antenna 10 corresponding to the constant switching stepof the tuning circuit 11 becomes large in a range where the resonancefrequency of the antenna 10 is high. On the other hand, the amount ofchange in the resonance frequency of the antennal 10 corresponding tothe constant switching step of the tuning circuit 11 becomes small in arange where the resonance frequency of the antenna 10 is low. Therefore,by making the switching step of the tuning capacitance be minimum or bytaking two steps at a time according to the search range as describedabove, excessively fine switching of the tuning capacitance can beomitted to shorten the process time needed for the search process.

In FIG. 5, a flowchart of the antenna adjustment process which isexecuted by the CPU of the control circuit 20 is shown. Hereinafter, theabove antenna adjustment process will be described in detail by usingthe flowchart.

For example, the antenna adjustment process is executed based on acommand which is inputted from outside in a setting adjustment processbefore being shipped out from a factory. Alternatively, the antennaadjustment process may be executed when a command to execute theadjustment process is given from outside via an operation unit (omittedfrom the drawing), for example, after the product shipment or may beexecuted when a normal receiving process cannot be carried outcontinuously because the receiving level is reduced during the radiowave receiving process.

When the antenna adjustment process is started, first, the CPU turns onthe feedback circuit 16 (step J1). Hereby, an oscillation signal offrequency which is approximately equal to the resonance frequency of theantenna 10 is generated at the antenna 10 and at the circuit section ofthe tuning circuit 11.

Next, the CPU switches the characteristic of the filter 13 to set areceiving channel (step J2). In the embodiment, for example, thecharacteristic of the filter 13 is switched in the order of 77.5 kHz→>60kHz→40 kHz.

When the receiving channel is set, next, the CPU calculates the searchrange corresponding to the receiving channel by formula (I) (step J3:search range deciding unit, calculation unit).

$\begin{matrix}{{Formula}\mspace{14mu} 1} & \; \\{\frac{1}{\left( {2\pi \times 1.1 \times f_{0}} \right)^{2}L} \leq C \leq \frac{1}{\left( {2\pi \times 0.9 \times f_{0}} \right)^{2}L}} & (1)\end{matrix}$

Here, C represents the search range which is converted to thecapacitance value of the tuning circuit 11, f₀ represents the frequencyof the desired wave of the receiving channel, L represents theinductance of the antenna 10, the coefficient “1.1” in left side and thecoefficient “0.9” in right side are error coefficients which are decidedfrom the acceptable error of the capacitative elements C0 to C9 and theinductance of the antenna 10. Here, the acceptance error of thecapacitative elements C0 to C9 and the inductance of the antenna 10 isset to 5%, and the above error coefficient is decided so that thesetting value for tuning the resonance frequency of the antenna 10 tothe frequency of the desired wave is surely included in the search rangeeven when the error of 5% occurs. When the acceptable error of each unitis different, the value of the above error coefficient can bearbitrarily changed according to the acceptable error.

In FIG. 6, a table showing an example of the search ranges correspondingto each of the receiving channels is shown. In FIG. 6, the value of theleast significant bit of the 9-bit counter corresponding to the minimumcapacitative element C0 is omitted as being a value of after the decimalpoint.

By the above calculation process of step J3, for example, when thereceiving channel is 40 kHz, the calculation is carried out by settingthe search range which is converted to the capacitance value of thetuning circuit 11 to “262.5 pF to 391.7 pF” as shown in the second rowin FIG. 6, and the counter value of the 9-bit counter corresponding tothe search range of “262.5 pF to 391.7 pF” is “125 to 201” in decimalnotation and is “01111101 to 11001001” in binary notation (value of theleast significant bit corresponding to the minimum capacitative elementC0 is omitted). Alternatively, a case when the receiving channel is 60kHz and a case when the receiving channel is 77.5 kHz are shown in thethird row and in the fourth row of the table of FIG. 6, respectively.

When the search range is calculated, next, the CPU sets the value of the9-bit counter which decides ON/OFF condition of the switches S0 to S8 tothe start value of the search range which is calculated in step J3 (stepJ4). For example, when the receiving channel is 77.5 kHz, the CPU setsthe value of the 9-bit counter to the start value “12” shown in the lineof “counter value range” in the fourth row of FIG. 6. Hereby, the totalcapacitance value which is to be in the connected condition in thetuning circuit 11 by the switches S0 to S8 being switched is set to theinitial value of the search range (converted to the capacitance value).

Next, the CPU carries out AD conversion to the detector output level andstores the value in the memory area A in the RAM (step J5).

Next, the CPU determines whether the receiving channel which iscurrently set is 40 kHz or not (step J6), and moves to step J8 when thereceiving channel which is currently set is not 40 kHz. However, whenthe receiving channel which is currently set is 40 kHz, the CPU carriesout a setting of the switch S0 corresponding to the minimum capacitativeelement C0 so as to be fixed to OFF (step J7) and moves to step J8.

In step J8, the CPU switches the switches among the switches S8 to S0which are set so as to vary by one step. That is, when the switch S0corresponding to the minimum capacity is set so as to be fixed to OFF,value of the 9-bit counter is updated by adding “1” to the low-ordersecond bit (or by adding “1” two times to the low-order 1 bit) of the9-bit counter which decides ON/OFF condition of the switches S8 to S0.On the other hand, when the switch S0 corresponding to the minimumcapacity is not set so as to be fixed to OFF, value of the 9-bit counteris updated by adding “1” to the low-order 1 bit of the 9-bit counter.

When the receiving channel is 60 kHz or 77.5 kHz, by updating thecounter value in the above step J8, connection of the first group oftuning condensers (C8 to C0) including the minimum capacitative elementC0 are switched and the total value of the tuning capacitance which isconnected to the antenna 10 is to be switched by minimum switchingsteps.

On the other hand, when the receiving channel is 40 kHz, by updating thecounter value in the above step J8, connection of the second group oftuning condensers (C8 to C1) excluding the minimum capacitative elementC0 are switched and the total of the capacitance value which isconnected to the antenna 10 is to be switched in order. That is, thetotal capacitance value is to be switched by minimum switching stepstaking two steps at a time.

In FIG. 7, a table which explains a difference between a case where theconnection of minimum capacitative element C0 is switched and a casewhere the connection of minimum capacitative element C0 is not switchedin the antenna adjustment process is shown.

As shown in the table of FIG. 7, in a case where the resonance frequencyof the antenna 10 is within a range of high frequency around 77.5 kHz,the total value of the tuning capacitance is switched by interval of 1.7pF when the minimum capacitance element C0 is set so as to be fixed toOFF. Thereby, the resonance frequency of the antenna 10 is to beswitched by an interval (for example, 800 Hz) which is too large(switching of the odd-number rows in the table of FIG. 7). Therefore, asdescribed above, when the resonance frequency of the antenna 10 iswithin a range of high frequency, the resonance frequency of the antenna10 can be switched by an adequate interval (for example, 400 Hz) byswitching the capacitance value of the tuning circuit 11 by minimumswitching steps, including the minimum capacitative element C0(switching of the second to the sixth row in the table of FIG. 7).

When the capacitance value is switched by updating the counter value,next, whether the counter value has reached the last value within thesearch range or not is determined (step J9). When the counter value hasnot reached the last value within the search range, the process returnsto step J5 and steps J5 to J8 are repeated. On the other hand, when thecounter value has reached the last value within the search range, theprocess exits the loop process of steps J5 to J9 and moves to next whichis step J10.

By step J4 and the loop process of steps J5 to J9, the setting of thetuning circuit 11 is switched within the search range which iscalculated for each of the receiving channels, and also, AD conversionis carried out to the detector output level every time the setting isswitched and the converted values are stored in the memory range A.

When each detector output level within the search range is stored andwhen the process is moved to step J10, the CPU compares the storeddetector output levels and obtains the counter value (switch settingvalue to decide the condition of switches S0 to S8) of when the maximumdetector output level was detected and stores this counter value in thememory region B of a RAM or a non-volatile memory by making this valueso as to correspond to the current receiving channel. The counter valueobtained here becomes the setting value of the tuning circuit 11 bywhich the resonance frequency of the antenna 10 is tuned to thefrequency of the receiving channel.

Next, the CPU determines whether the current receiving channel is thelast channel (40 kHz) or not. When the current receiving channel is notyet the last receiving channel, the process returns to step J2 and stepsJ2 to J10 are repeated. By repeating these steps, the setting value ofthe tuning circuit 11 by which the resonance frequency of the antenna 10is made to tune to the frequency of the receiving channel can beobtained for all to the plurality of receiving channels (77.5 kHz, 60kHz, 40 kHz).

Then, when the process is finished for all of the receiving channels,the process proceeds to YES in step J11 to turn off the feedback circuit16 (step J12). Hereby, the oscillation signal at the antenna 10 and atthe circuit section of the tuning circuit 11 stops. Then, the antennaadjustment process ends.

[Radio Wave Receiving Process]

The radio wave receiving process is started in a state where each of theoptimum setting values of the tuning circuit 11 corresponding to theplurality of receiving channels are respectively stored in the memoryregion B by the antenna adjustment process. In the radio wave receivingprocess, the feedback circuit 16 will not be in operation state. Whenthe radio wave receiving process is started, the CPU identifies areceiving channel of the standard radio wave based on controlinformation of different system and switches the setting of the filter13 so as to suit the receiving channel. Further, the optimum settingvalue of the tuning circuit 11 corresponding to the current receivingchannel is read out among data stored in the memory region B by theantenna adjustment process and this value is set to the 9-bit counterwhich decides the connection condition of the switches S0 to S8. Then,the switches S0 to S8 are switched and the resonance frequency of theantenna 10 is tuned to the frequency of the current receiving channel.

Further, by starting the receiving operation in the above condition, thestandard radio wave is received by the antenna 10 by high receiversensitivity, and the received signal passes through the RF circuit 12,the filter 13 and the amplifier 14 to be detected at the detectorcircuit 15. Then, the detected time code signal is outputted and, forexample, is read by the control circuit 20.

As described above, according to the radio wave receiver 1 of theembodiment, at the time of the antenna adjustment process, the searchrange in which the setting of the tuning circuit 11 is to be switched isnarrowed down to a portion of the entire adjustable range according tothe frequency of the desired wave. Therefore, the search process(process to switch the setting of the tuning circuit 11 while monitoringthe detector output level) of the unneeded portion of the adjustablerange where optimum setting condition of the tuning circuit 11 cannot befound can be omitted. Thereby, process time of the antenna adjustmentprocess can be shortened greatly.

Moreover, according to the radio wave receiver 1 of the embodiment,because the search process in the unneeded portion of the adjustablerange where optimum setting condition of the tuning circuit 11 cannot befound is omitted, as shown in FIG. 4, an advantage in whichinconvenience of erroneously obtaining the optimum setting condition ofthe tuning circuit 11 due to noise N can be avoided even when a greatnoise source exists in the frequency outside of the search range, forexample.

Further, according to the radio wave receiver 1 of the embodiment, thetuning circuit 11 has a broad adjustable range in which the antenna 10can be tuned to all of the frequencies of a plurality of receivingchannels. On the other hand, at the time of antenna adjustment process,the search process of each receiving channel is carried out only withinthe search range corresponding to each receiving channel. Therefore,process time of the antenna adjustment process can be remarkablyshortened comparing to the case where the search process is repeatedlycarried out within the entire adjustable range in the setting of aplurality of receiving channels.

Furthermore, even when the circuit constant of the antenna 10 and thetuning circuit 11 is deviated by the maximum acceptance error, the abovedescribed search range is calculated so as to include the adjustmentpoint where the resonance frequency of the antenna 10 is made to tune tothe frequency of the desired wave. Therefore, the optimum settingcondition of the tuning circuit 11 can be obtained surely.

Moreover, according to the antenna adjustment process of the embodiment,because the search range is calculated and obtained from the frequencyof the desired wave by the CPU carrying out the arithmetic processing, amemory region for storing information indicating the search range inadvance is not needed, and even when there is a change in the frequencyof the received channel or the acceptance error of the circuit elements,the process can easily react to the change by merely changing thevariable value of the arithmetic expression.

In FIG. 8, a diagram showing an example of data stored in ROM 21 in aradio wave receiver of other embodiment is shown. Here, in the aboveembodiment, the search range is obtained by the arithmetic processing.However, as shown in FIG. 8, the search range data (information ofspecific adjustable range) 211 in which data indicating the search rangeis registered so as to correspond to each receiving channel may bestored in the ROM (storage unit) 21 in advance, and the data of thesearch range may be read and decided from the search range data 211 atthe time of deciding the search range. According to such structure, thestructure needed for carrying out the arithmetic processing to obtainthe search range is not needed. Further, it is advantageous becausepower consumption due to the arithmetic processing can be reduced whenthe antenna adjustment process is carried out when the apparatus isdriven by a battery.

Further, according to the radio wave receiver 1 of the above embodiment,the capacitance value of the tuning circuit 11 is to be switched byminimum switching steps at the time of search process of the receivingchannels of 77.5 kHz and 60 kHz. In contrary, at the time of searchprocess of the receiving channel of 40 kHz, the capacitance value of thetuning circuit 11 is to be switched by minimum switching steps takingtwo steps at a time by setting the minimum capacitative element C0 so asto be fixed to OFF. Therefore, the resonance frequency of the antenna 10can be changed by an adequate interval even when the resonance frequencyof the antenna 10 is within a high range or when the resonance frequencyof the antenna 10 is within a low range. Thereby, process time of theantenna adjustment process can be shortened comparing to the case wherethe search process is carried out by needlessly switching the resonancefrequency of the antenna 10 by a fine interval.

Furthermore, the search process is carried out by switching the firstgroup of tuning condensers formed of all of the capacitative elements C0to C8 in which the connections can be switched within the search rangecorresponding to the receiving channels of 77.5 kHz and 60 kHz. On theother hand, the search process is carried out by switching the secondgroup of tuning condensers formed of capacitative elements in which theminimum capacitative element C0 is excluded from the plurality of thecapacitative elements C0 to C8, in which the connections can be switchedwithin the search range corresponding to the receiving channel of 40kHz. Therefore, switching of the capacitance value of the tuning circuit11 suited to the search range can be realized without overlycomplicating the switching pattern of the setting of the tuning circuit11.

Here, the present invention in not limited to the above embodiment, andvarious modifications can be carried out. For example, in the aboveembodiment, the CPU determines whether the resonance frequency of theantenna 10 approximated the frequency of the desired wave or not bymonitoring the output level of the detector circuit 15. However, forexample, the above determination may be carried out by directlymonitoring the level of the signal which passes through the filter 13.Further, when automatic gain control of the RF circuit 12 and theamplifier 14 is carried out in order to stabilize the output of thedetector circuit 15, the determination of whether the resonancefrequency of the antenna 10 approximated the frequency of the desiredwave or not and whether the oscillation signal passed through the filter13 or not may by carried out by monitoring the automatic gain control.

Further, in the above embodiment, it is described that an adjustablerange of the tuning circuit 11 in which the resonance frequency of theantenna 10 can be tuned to the frequency of the desired wave even whenthe inductance of the antenna 10 and the capacitative elements of thetuning circuit 11 have error which is the maximum acceptance error isapplied as the search range. However, the search range may be set sothat the search range will be minimum range within a range where theabove condition can be fulfilled or the search range may be set so as tobe slightly broader to allow leeway.

Furthermore, in the above embodiment, the search process is carried outfor the entire search range. However, when the peak of the detectoroutput level is detected during the search process, the search processcan be stopped at this stage and the setting condition of the tuningcircuit 11 when the peak of the detector output level was detected maybe applied as the optimum setting condition. Further, in the aboveembodiment, all of the AD converted values of the detector output levelsare stored to obtain the setting value of the tuning circuit 11 in whichthe maximum detector output level was obtained by comparing the storedvalues. However, by carrying out a comparing process every time when anew AD conversion value is obtained by comparing the new AD conversionvalue to the stored AD conversion value and by saving the AD conversionvalue which is larger in a memory region, the setting value of thetuning circuit 11 in which the detector output level is at the peakwithin the search region may be obtained.

Moreover, in the above embodiment, an example where only two types ofchanging is carried out in the switching of the tuning circuit 11, onetype being switching by minimum switching steps and another type beingswitching by minimum switching steps taking two steps at a time, isshown. However, patterns of taking multiple steps at a time such asswitching by minimum switching steps taking three steps at a time ortaking four steps at a time may be added. Further, changing patterns oftaking multiple steps at a time such as alternatively carrying outtaking two steps at a time and taking three steps as a time and the likemay be added.

Moreover, in the above embodiment, the number of steps to be taken at atime in the switching of the tuning circuit 11 is changed for each ofthe receiving channels. However, when the search process is carried outby switching the setting of the tuning circuit 11 for a broad searchrange with respect to one receiving channel, the number of switchingsteps to be taken at a time and the patterns may be changed for parts ofthe search range.

Moreover, in the above embodiment, an example where the presentinvention is applied to a receiving circuit of straight format is shown.However, the present invention can be similarly applied to receivingcircuits of super heterodyne format and direct conversion format.Further, the details shown in the above embodiment such as the numberand types of receiving channels, the number of capacitative elements ofthe tuning circuit, ratio of each capacitance value of the tuningcircuit and the like can be arbitrarily changed within the scope of thepresent invention.

The entire disclosure of Japanese Patent Application No. 2009-133686filed on Jun. 3, 2009 including descriptions, claims, drawings, andabstracts are incorporated herein by reference in its entirety.

1. A radio wave receiver, comprising: an antenna to receive a radiowave; a tuning unit to switch a frequency characteristic of the antennain a stepwise fashion; a positive feedback unit to oscillate the antennaand a circuit section of the tuning unit by applying a positive feedbackto a signal path including the tuning unit; a switching unit to turn afeedback operation of the positive feedback unit on or off; a receivingprocess unit to carry out a signal process by extracting a signal of adesired wave among received signals which are received from the antenna,in a state in which the feedback operation of the positive feedback unitis turned off; a search control unit for causing the positive feedbackunit to generate an oscillation signal at the circuit section andsearching for a setting condition of the tuning unit in which theoscillation signal is extracted in the receiving process unit whileswitching a setting of the tuning unit, in a state in which the feedbackoperation of the positive feedback unit is turned on; and a search rangedeciding unit to selectively decide an adjustable range in which theswitching of the setting of the tuning unit is carried out by the searchcontrol unit so as to be a specific adjustable range which is a portionof an entire adjustable range of the tuning unit corresponding to afrequency of the desired wave according to the following formula (1):$\begin{matrix}{\frac{1}{\left( {2\pi \times 1.1 \times f_{0}} \right)^{2}L} \leq C \leq \frac{1}{\left( {2\pi \times 0.9 \times f_{0}} \right)^{2}L}} & (1)\end{matrix}$ wherein: C is the specific adjustable range, which isconverted to a capacitance value of the tuning unit; f_(o) is thefrequency of the desired wave of a receiving channel; L is an inductanceof the antenna; and coefficients 1.1 and 0.9 are error coefficientswhich are decided from acceptable errors of a capacitative element andthe inductance of the antenna.
 2. The radio wave receiver according toclaim 1, wherein the receiving process unit is structured so as to carryout the signal process to each signal of the desired wave of a pluralityof receiving channels by switching the receiving channels, and thesearch range deciding unit decides the specific adjustable range so asto correspond to each frequency of the desired wave of the plurality ofreceiving channels.
 3. The radio wave receiver according to claim 2,wherein the search range deciding unit comprises a computing unit tocalculate the specific adjustable range for tuning the frequencycharacteristic of the antenna to the frequency of the desired wave, andthe search range deciding unit decides the specific adjustable rangecorresponding to each of the plurality of receiving channels based on acalculation result of the computing part.
 4. The radio wave receiveraccording to claim 2, wherein the search range deciding unit comprises astorage unit in which information of the specific adjustable rangecorresponding to each of the plurality of receiving channels is stored,and the search range deciding unit selects the specific adjustable rangecorresponding to each of the plurality of receiving channels from theinformation in the storage unit.
 5. The radio wave receiver according toclaim 1, wherein the search range deciding unit decides a rangeincluding an amount of variance of the setting condition of the tuningunit based on an acceptable error of a circuit constant from the settingcondition of the tuning unit where a resonance frequency of the antennais most approximated to the frequency of the desired wave when theantenna and the tuning unit have an ideal circuit constant as thespecific adjustable range corresponding to the frequency of the desiredwave.
 6. The radio wave receiver according to claim 1, wherein thetuning unit comprises a plurality of tuning condensers which connectwith a signal line of the antenna and a plurality of switches to switchconnection conditions of the plurality of tuning condensers, and thetuning unit is structured so that the frequency characteristic of theantenna is changed in the stepwise fashion by switching the plurality ofswitches.